no issue
`ember-light-table` is falling behind Ember.js and other addon development and is increasingly causing issues with Ember deprecations and addon incompatibility.
- swaps `ember-light-table` usage for a straightforward table using `vertical-collection` for occlusion
- uses the same loading mechanism as the members screen with a slight optimisation where the initial load will fetch subscribers in batches of 200 until they are all loaded
- removes now-unused pagination mixin
- fixes duplicate subscriber validation handling
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